This proposal discusses the production and implementation of peptide/ recombinant antigens for the development of a serological assay for the diagnosis of human granulocytic ehrlichiosis (HGE). HGE has recently become recognized as a major tick-borne pathogen of humans in both the United States and Europe. Delays in diagnosis and treatment can result in increased morbidity and mortality, which has been estimated to be as high as 7-10% with elderly patients being more prone to both severe infection and death. Diagnostics tests for HGE are labor intensive, expensive and time consuming and results can be complicated by Co-infection of patients by the tick-borne pathogens of human babesiosis and Lyme borreliosis, or by other infections or autoimmune diseases. Because treatment for the various tick-borne diseases differs, and delays in treatment can lead to increased morbidity, there is a need for a good, rapid diagnostics tool for HGE. Immunodominant HGE antigens that are both sensitive and specific have already been isolated at Corixa by expression screening. The combination of these recombinants, an extensive serum bank, and a collaboration with a key investigator in the area of tick-borne diseases, should enable the goals and objectives of this proposal to be achieved. PROPOSED COMMERCIAL APPLICATION: The proposed studies will lead to commercialization of a diagnostic test for improved differential diagnosis of human granulocytic ehrlichiosis (HOE) in the presence of other tick-borne infections such as Lyme disease and human babesiosis. The estimated worldwide market for such a test should be similar to that for Lyme disease testing both in the U.S. and worldwide. Current estimates for this market are $30-50 million per year.